1. Field of the Invention
This invention relates generally to a machine including a rotatable drum for extracting liquid out of liquid absorbent goods received in the drum during rotation of the drum at high speeds. Specifically, this invention relates to improvements in such machines having systems for at least partially balancing the drum to correct imbalances due to unequal distribution of goods about its inner circumference.
2. Description of the Prior Art
In a machine of this type, typically a washer/extractor, the drum is contained in a housing which is supported by a frame. The drum rotates about its axis at relatively slow speeds during the initial cycles of washing and at high speeds during a final cycle in order to extract the liquid from the goods. The lower speeds range from less than 20 to 65 revolutions per minute (rpms) while the high speeds can reach in excess of 1,000 rpms.
Most machines are designed to withstand the unavoidable vibration due to the high speed revolution of the drum. During such high speeds, liquid absorbent goods are plastered against the side of the rotating drum. Very rarely are the goods evenly distributed about the drum. Thus, an unequal distribution of weight will create an imbalance which can over time cause severe damage to the washer/extractor including the structure supporting the housing and the mechanism rotating the drum.
Several attempts have been made to compensate for the imbalance to prevent damage to the machine in rigid mount models. The difficulties associated with finding a solution for the imbalance problem include identifying the magnitude of an imbalance, identifying the location of the imbalance in the rotating drum, and offsetting the imbalance during the extraction process.
One such attempt is described in U.S. Pat. Nos. 2,534,267/268/269, Kahn, et al wherein the drum includes three inwardly directed hollow ribs, which are spaced about the drum to function not only as lifters for tumbling the goods, but also as balancing compartments for receiving a balancing fluid. Balancing fluid is independently injected into each compartment by balancing fluid injection valves that are selectively activated to inject balancing fluids into the respective compartments to compensate for any imbalance.
These Kahn systems utilize a magnetic vibration pick up device to determine the magnitude of an imbalance during an extraction cycle. This device is a fixed reference device in that part of it is mounted on the vibrating housing or frame supporting the drum, while the other part is mounted at a point which is fixed relative to the vibrating frame. A distributor disk or commutator whose rotation is synchronized with that of the rotating drum is used to identify the location of the imbalance. A solenoid or actuation mechanism of the balancing fluid injection valve is actuated by the simultaneous receipt of signals from the magnetic vibration pick up device and the distributor disk.
One problem with the Kahn system is expansion and contraction of cooperating parts of the vibration pick up device due to wear, settling, and temperature changes, necessitating constant adjustments. Another problem with this system is that the energizing means actuates the balancing fluid injection valve with each revolution of the drum. Balancing fluid passes through the valve during the entire revolution of the drum even though the valve is only actuated for a short time during the revolution because the mechanical response time closing the valve is slower than the electrical response time. The service life of the valve is significantly reduced by wear on the valve due to the repeated actuation of the valve during each rotation of the drum.
Yet another problem associated with the Kahn system is that it is inflexible with respect to choosing which balance compartments are actuated and when they are actuated. Once the system is designed and constructed, only specific injectors are activated relative to certain imbalances. If a user finds that different injectors should be actuated or that more than one should be actuated at a time, he cannot do this without significantly changing the system.
Still another problem is that the balancing system provides no way to terminate the extraction process if the imbalance exceeds permissible limits. Sometimes an imbalance reaches a level incapable of being balanced by the balancing system, at which point the speed of the machine should be reduced so the liquid absorbent goods can be redistributed around the drum to avoid damage to the machine.
Finally, the sensitivity and accuracy of the Kahn system is limited to the resolution of the commutator which has a cam operated switch for each of the balancing valves. For example, when an imbalance is not directly opposite a rib, two ribs will simultaneously be injected. Whereas, if the imbalance is directly located opposite a rib, only that rib will be injected. The accuracy of this process is dependent on the sensitivity of these mechanical switches.
U.S. Pat. No. 3,117,962, Starr discloses a machine having a system designed to overcome some of the problems of the Kahn systems. It has a mechanical vibration sensing device incorporating a fluid filled container, mounted in a fixed position relative to the vibrating frame, and closed on one side by one moveable member positioned to be displaced by vibrations of the drum and on the other side by a second moveable member displacement which actuates a mechanical switch. This mechanical vibration sensing device also incorporates an orifice (placed below a reservoir) which prevents slow movements of the vibration detection side from actuating the mechanical switch, while high speed motions would be transmitted, due to the viscosity of fluid in the container. As a result the unit is self compensating for wear, settling, and environmental changes and therefore does not require constant adjustment. Although a commercially successful modification of the machine disclosed in the Kahn patent, the latter machine nevertheless suffers from at least certain of the problems mentioned above. In addition, its sensing device requires several additional mechanical parts which can fail over time.
Additionally, the housings of the machines described in Kahn and Starr are rigidly mounted so whatever residual imbalance remains in the machine after the balance sequence is transmitted to the structure supporting the frame. Thus, installation of these machines is limited to structurally sound environments. Later, the machine of the Starr patent was further modified to flexibly support its housing, wherein the housing becomes a spring supported mass, in order to isolate the vibration so the machines were capable of being installed in less structurally sound environments.
In a rigid mount machine, the amount of excursion of the frame relative to a fixed position in space is linear with respect to the vibration force created. On the other hand, a flexibly supported machine undergoes a transition where the spring supported mass system experiences a resonant condition as the rotating drum accelerates from the lower speed ranges to the higher speed ranges. This resonant condition produces excursions which are extreme compared to the movements of a rigid mount machine. Even after the machine accelerates through its resonant frequency (at approximately 100 rpm) the amount of excursion of the spring supported mass relative to a fixed point in space is far greater than that of a rigidly mounted machine.
Since the fixed reference, vibration sensing mechanisms in both the Kahn and Starr machines were designed to measure very small displacements that occur in the rigid mount system, excursions generated in a flexibly supported machine would destroy them. Thus, the fixed reference device of the modified Starr machine has required complex changes.
It is the primary object of this invention to provide a machine of the type described, and particularly one in which the housing is flexibly mounted, in which these and other problems are overcome.
Another object is to provide such a machine having a balancing system which is of such construction that large initial excursions may be detected in a simple and inexpensive manner and without risk of damage.
A further object is to provide such a machine having a balancing system in which the proper balancing compartments are determined and then filled in such a manner as to reduce wear on the parts of the system as well as to reduce the number and likelihood of malfunctions of the parts.
It is another object of the present invention to provide such a machine having an improved balancing system which prevents damage to the machine when the load cannot be balanced because the imbalance exceeds a maximum allowable level.
It is yet another object of the present invention to provide such a machine having an improved balancing system where the choice of which and when balancing ribs are injected with fluid is not limited to the mechanical constraints of the machine.
It is still another object of the present invention to provide such a machine having an improved, more accurate and sensitive balancing system.